Continued efforts have been made to delineate the genetic mechanisms underlying virulence of rotavirus in the newborn gnotobiotic piglet model. In addition to the gene encoding rotavirus outer capsid protein VP4 or VP7, the tenth gene appears to play an independent role in determining the virulence of rotavirus in the porcine model. Elucidation of the constellation of genes required for rotavirus virulence may have important implications for the development of effective rotavirus vaccine strategies.